936643 ÷ 21 
The aim is to understand the frequency of 21 in 936643.

Step 1:
The number 21 fits into 9 0 times, leaving a remainder of 9.
Record the quotient 0 as the next digit in the result. 
Result so far: 0.0
If we subtract 0 from 9, we get 9.
Include the next digit (3) from the dividend after 9, then repeat: 93 / 21

Moving on to step 2:
If we divide 93 by 21, we get 4 and a remainder of 9.
The number 4 becomes the next digit in our result. 
Result so far: 4.0
If we take 84 away from 93, we end up with 9.
Take the next digit (6) from the dividend and append it to 9, then repeat: 96 / 21

Moving on to step 3:
96 divided by 21 is 4 with a remainder of 12.
The number 4 becomes the next digit in our result. 
Result so far: 44.0
Subtract 84 from 96 to get 12.
Grab the next digit (6) from the dividend, add it to 12, then carry on: 126 / 21

On to step 4:
When dividing 126 by 21, we get 6 with a remainder of 0.
The number 6 becomes the next digit in our result. 
Result so far: 446.0
Subtract 126 from 126 to get 0.
Grab the next digit (4) from the dividend, add it to 0, then carry on: 4 / 21

Going ahead to step 5:
The number 21 fits into 4 0 times, leaving a remainder of 4.
Use 0 as the next digit of our solution. 
Result so far: 4460.0
Deduct 0 from 4 and we're left with 4.
Bring next digit (3) of the dividend behind the 4 and repeat the process: 43 / 21

Let's proceed to step 6:
21 goes into 43 2 times with a remainder of 1.
The next digit of our result is 2. 
Result so far: 44602.0
Deduct 42 from 43 and we're left with 1.
Since there are no more digits in the dividend, we add a zero to the remainder making it 10, and continue the process.

Let's proceed to step 7:
If we divide 10 by 21, we get 0 and a remainder of 10.
The next digit of our result is 0. 
Result so far: 44602.0
Deduct 0 from 10 and we're left with 10.
Since there are no more digits in the dividend, we add a zero to the remainder making it 100, and continue the process.

Moving on to step 8:
21 goes into 100 4 times with a remainder of 16.
Use 4 as the next digit of our solution. 
Result so far: 44602.04
If we subtract 84 from 100, we get 16.
Since there are no more digits in the dividend, we add a zero to the remainder making it 160, and continue the process.

Let's proceed to step 9:
When dividing 160 by 21, we get 7 with a remainder of 13.
The next digit of our result is 7. 
Result so far: 44602.047
Subtract 147 from 160 to get 13.
Since there are no more digits in the dividend, we add a zero to the remainder making it 130, and continue the process.

Moving on to step 10:
If we divide 130 by 21, we get 6 and a remainder of 4.
The next digit of our result is 6. 
Result so far: 44602.0476
If we subtract 126 from 130, we get 4.
Since there are no more digits in the dividend, we add a zero to the remainder making it 40, and continue the process.

Let's proceed to step 11:
21 goes into 40 1 times with a remainder of 19.
Write down 1 as next digit of the result. 
Result so far: 44602.04761
Subtract 21 from 40 to get 19.
Since there are no more digits in the dividend, we add a zero to the remainder making it 190, and continue the process.

Step 12:
If we divide 190 by 21, we get 9 and a remainder of 1.
The next digit of our result is 9. 
Result so far: 44602.047619
Subtracting 189 from 190 leaves us with 1.
Since there are no more digits in the dividend, we add a zero to the remainder making it 10, and continue the process.

Step 13:
21 goes into 10 0 times with a remainder of 10.
The next digit of our result is 0. 
Result so far: 44602.047619
If we subtract 0 from 10, we get 10.
Since there are no more digits in the dividend, we add a zero to the remainder making it 100, and continue the process.

Moving on to step 14:
The number 21 fits into 100 4 times, leaving a remainder of 16.
Use 4 as the next digit of our solution. 
Result so far: 44602.04761904
Subtracting 84 from 100 leaves us with 16.
Since there are no more digits in the dividend, we add a zero to the remainder making it 160, and continue the process.

The quotient of the division is 44602.04761904, and the remainder is 1.6e-08.